The IONICON Liquid Calibration Unit (LCU) evaporates aqueous standards into a gas stream, resulting in a gas flow containing compounds at defined trace concentrations. This gas can be used for precise calibration of trace gas analyzers over an extensive range of compounds and concentrations.

The preparation of an aqueous standard mixture is simple, can be done immediately, and for a large variety of compounds. IONICON’s LCU is a cost-effective and highly versatile calibration device for trace gas analyzers that can be implemented in many fields of research, such as food and flavor, biotechnology, breath-gas analysis, environmental research, and petrochemical analysis.

Setup for Efficient Evaporation

The LCU uses an optimized evaporation technique that can be used for volatile as well as semi-volatile compounds. They key component is the purpose-built nebulizer: a gas and liquid flow mix at the tip of the nebulizer producing a fine mist. These micro-droplets are ejected into a heated (> 100°C) evaporation chamber (see figure above), which facilitates the evaporation process.

This system has several advantages:

The evaporation of compounds with a slow evaporation rate is enhanced by the enlarged surface area of the droplets.

And, compounds which are dissociated in water, such as acids (or bases), experience a decreasing pH value when the water evaporates from a droplet. This in turn reduces the dissociation and leads to a total evaporation of the compound.

Range of Compounds and Concentration

The LCU can be employed for calibration of trace gas analyzers over an extensive range of compounds and concentrations.

Solubility

For trace concentrations, a very low solubility of a compound in water is sufficient to produce an aqueous standard. As an example, this has successfully been achieved for propofol which has a solubility of only 0.12 g/l (25 °C) in water.

Vapor pressure

The efficient evaporation mechanism enables calibration of compounds even with very low vapor pressures (i.e. semi-volatiles). This has successfully been demonstrated for caffeine and indole (vapor pressure of only 1.6 Pa at 25 °C), which set the current benchmark.

The LCU has successfully been used with a growing variety of compounds, including ketones, aldehydes, alcohols, amines, terpenes, organic acids, and esters.

Concentration Range

The LCU has a dynamic range of 100. The resulting concentration in the gas phase is directly dependent on the concentration in the aqueous standard. This allows to explore concentrations up to ‰ or even % and down to the pptv range and below.

Specifications: LCU-s vs. LCU-a

The LCU is available in two versions:

The LCU-s (standard) has one port for a liquid flow and one port for the dilution gas flow.

The LCU-a (advanced) has an additional liquid port, which can be used to connect pure water in order to maintain the total liquid flow and thus keep the sample gas humidity constant. Alternatively, two liquid standards can be connected. Additionally, the LCU-a is equipped with a mass flow controller (passivated by SilkoNert2000) to admix gaseous calibration standards or CO2.